CurtPalme.com Home Theater Forum

[wendortb]

Register to remove this ad. It's free!

I have a house that has a multipurpose room that contains my home theater. I have been living with a noisy forced air heating and air conditioning system. I am hoping someone on here has some insight into ways to quite this down. I am working on turning my theater 90 degrees which will put me alot closer to the furnace. In the picture, I will be sitting under the beam, my second row will be even closer to the furnace.

The top left corner of the picture shows where my hvac system and water heater are located. This is a closet with 2 bifold closet doors that have slats in them on the 6'3" section.

Right now, at my seating position on the couch, the furnace is about 58db. Getting kind of close to the furnace it is 70db. Really it is the cold air return that is giving me most of the noise. The front of the furnace is bearable, but just around the corner, (the 3' 3.5" section of the closet) is extremly loud. At the bottom of this wall is the cold air return vent. This vent is rather large, I don't have the specific dimentions but it is something like 30 x 16. Seems large enough for my 1400 sq ft house. There is also a cold air return upstairs. Behind the vent is about 8" straight of duct work, then you are in the area of the furnace. The blower motor is in this section of the furnace. The blower faces the cold air return. This is all straight through and I can literally stick my arm into the blower motor if the vent cover is off (and the filter is removed).

I checked this out about a year ago, and at that time I found it to mostly be the blower making the noise. It is just the sound of air rushing. I removed the cover for the cold air return, and didn't notice much difference.

I took the blower out and cleaned it, but this didn't help. I looked around the circuit board for the blower motor, but don't see any way to slow down the blower. At least nothing that is labeled anyway.

I am trying for a cheaper solution here. My only thought right now is to line the short 8" duct with some duct insulation. Then around the area (there is a doorway next to the vent that leads outside, and a fridge right across from the vent) put some acoustic panels that may help absorb the sound.





Let me know if you need any specs like the furnace model or anything. My digital cam died so sorry, no pics. I hope someone can help quite this beast down for cheap.

[wendortb]

OK, I just had a thought right after posting this.

What about if I put up a sliding wall that slides from infront of the furnace closet, to the area where the cold air return and freezer are. This will still allow me to use the back door when needed, but should reflect enough of the sound away from the listening position to be bearable. I may try putting up a sheet of roofing insulation (2"thick hard foam) I got for free to see how this works. I can just lean it against the closet for a temporary solution.

My only problem with this, is that I was going to put my right surround speaker on top of the fridge. This panel will then block some of the sound of that surrond speaker. My surrounds are onix RSS300 dipole speakers.

BTW, I know the ideal way to deal with this would be to replace the blower with a quiter one, but this setup is temporary. Once I finaly build a house (in about 5 years or so) I will create my ideal room, without a furnace sitting in the room.

[greg_mitch]

If there is space inside the mechanical closet put a botted return on the return vent with duct liner.

I am assuming right now it is just a grille in the wall and no ductwork behind it.

This will help to cut the noise.

Also if the closet doors are slatted, and the return grille is not ducted, you are pulling air from there as well. Perhaps after you duct the return you could cut some 7'x3' sections of duct liner and just tack to the inside surface of the slatted doors to kill any sound bouncing around in there.

Are the walls of the closet all the way up to the structure above? If they aren't they should be.

Maybe an actual picture would help.

[ecrabb]

The foam insulation won't do anything at all. You need broadband absorption, and the foam insulation has no absorptive properties. Something with mass would provide some isolation - say, drywall for instance - but, you'd need to contain it. Since you need to allow the air to move, that won't work.

If most of the noise is coming from the return intake, you could build some sort of lined and baffled box to allow the air to flow but absorb the turbulence noise. Depending what a "box" would look like in the space, you could even destroy a piece of furniture to line with duct liner to mount against the wall. Think of something like a toy box or bench seat. Remove the bottom, line the box with duct liner, and mount to the wall high enough to provide a space at the bottom with the same cross-sectional area the original intake has. The air still moves, but a lots of the noise gets absorbed.

As for the louvered doors, that probably provides combustion air for the furnace and water heater, so you can't cover them. What you could do is put some accordion-style room dividers with absorptive material on the side facing the closet out a couple feet from the closet.

You should be able to knock those two projects out in a weekend and they should cut your noise significantly.

SC

[wendortb]

[Chuck27]

In my experience, the midrange and higher frequencies can be attenuated by making the the air flow turn a couple of corners. A baffle box like SC mentions would be a great place to start. High frequency sounds don't like to turn corners.

I am working on a similar problem in my own house with a furnace room next to the theatre and I'm concentrating on acoustically isolating the furnace room while still allowing enough air to get in so it doesn't starve. An oil furnace that is starved for air gets ugly very quickly.

Chuck

[wendortb]

[mhalsan]

If this is a gas furnace, there might be two motors: the main fan and a smaller, high-speed combustion air blower.
The main fan can be slowed down with a fan speed control under certain circumstances, but with caution: if the temp rise through the unit gets too high, the heat exchanger's life can be shortened. In general, I wouldn't want the discharge air to exceed about 120 degrees.
The gas manifold pressure can be reduced slightly to keep the rise to a reasonable level, however this will also reduce heat output. Typical manifold pressure is 3.5" water column. I have successsfully ran the pressure as low as 2" without ignition problems.
The combustion air blower can't be altered, there's a risk of flame roll-out and/or carbon monoxide production.
I'd recommend having an HVAC tech on hand to help with this mod. Any combustion appliance can become dangerous if not set up properly.

Another option involves shutting the furnace down during a movie. Many receivers or pre/pro units have 12VDC outputs. This output could operate a small relay with a normally-closed contact, which would interrupt the thermostat conductor tied to the "W" terminal on the furnace. When the relay energizes, the contact opens, and the call for heat would be removed. The 12V output on the receiver could be programmed in a number of ways, probably a softkey on a programmable remote would be the most useful. The furnace would operate normally when the receiver is turned off. This method would not involve any mods to the furnace.

Thanks, Mark

[wendortb]

[wendortb]

ok, got some measurements & such. The duct work, from the outside of the drywall to the actual furnace is 10" deep. The opening in the drywall where the cover is 27.75"x13.75". The opening on the furnace is 23"x14.5". Just in front of the cold air return, I am registering 78db. In front of the closet doors I get 72db. I didn't think that much sound came out of the closet doors, but I guess so.



Here you can see where the closet, door, and fridge are located. At the bottom of the closet there on the side is the cold air register.


Here is a pic of the ductwork of the cold air return. At the back of there is my furnace filter.



I am going to try the 2" foam infront of the area and see why my spl meter reads.

[greg_mitch]

Holy cow you don't have any room there.

I was actually saying booted return, not bottled return. I can't type. It is a baffle box like SC mentioned as well.

You don't have a lot of room there though.

Does the sound of the cold air return greatly reduce when the grille is removed? Maybe the return grille is undersized?

Perhaps you can make it larger so there isn't such a large pressure drop across it? Or change grille types, something with a larger free area. Like an eggcrate type? Do you by chance know how much CFM is going through the grille? Maybe some info on the furnace blower would clue you in.

If you give me the CFM I could maybe look up a grille with better sound characteristics?


JUst a thought.

[AnalogRocks]

Why not try two pannels that extend 2/3rd's of the way across your cold air return? Put one at the front and one a couple of inches away from the filter. Just for testing. Maybe wrap them in foam and see if that quiets anything down.

It's like the baffling in a car muffler, you don't want to ubstruct the air flow too much but you need to break up the sound waves.

Oh and just for safety, take a piece of the foam you want to use, outside, and do a fire check on it. You may find it goes up with a 'Wooooofff'. Some foams do that and other's burn more slowly. Could be the difference between getting out in a fire and not.

[AnalogRocks]

Why not try two pannels that extend 2/3rd's of the way across your cold air return? Put one at the front and one a couple of inches away from the filter. Just for testing. Maybe wrap them in foam and see if that quiets anything down.

It's like the baffling in a car muffler, you don't want to ubstruct the air flow too much but you need to break up the sound waves.

Oh and just for safety, take a piece of the foam you want to use, outside, and do a fire check on it. You may find it goes up with a 'Wooooofff'. Some foams do that and other's burn more slowly. Could be the difference between getting out in a fire and not.

[wendortb]

greg_mitch: I know I don't have any room, that is why I was looking at sound deflection and absorbtion. I checked the spl of the cold air return with the grill on and off. With the grill on it is actually 1 db quieter 2 foot from the cold air return. Because of this, I don't think it is undersized. I will try to find the model number tomorrow and get it to you.

AnalogRocks: I will try the foam idea. Good point with the foam. I think for the permanent installation, I will probably go with something that is rigid fiberglass. That way I am sure it doesn't burn and it is rigid enough to stand on it's own. It will also absorb some sound too. Maybe a ceiling tile or something. I don't know, I will have to do more research as to what they use in the HVAC ducts. Would definitely suck if a fire broke out.

I really appreciate the help. I will try to find the furnace model info.

[wendortb]

I got the following information off the blower, I also saw the same model number listed on a sicker on the furnace, I didn't see any other info on the furnace for a model number. I listed the numbers that were listed for lp, since that is what I have.

Goodman Manufacturing Company L.P.
GMP125-4
Cat. 1
Heating Input (Btu/Hr) 100,000
Output Capacity (But/Hr) 80,000
Tempurature Rise of F 45-75
Manifold Pressure (In W.C.) 10
External Static Pressure (in W.C.) .20
Motor 1/2 hp
Blower (in) 10x10
Aux Limit Set (F) 135
Max Gas Supply to furnace (in W.C.) 14
Certified 1993

I am sure you didn't need all that info, and there is probably something you need that I didn't write down. But that is what looked interesting to me.

I searched around the internet a little, and I think I did find where they sell a replacement circuit board. Can anyone look at this and tell me how you set the fan speed differently on this board? I would like to look to see what speed mine is set at for starters, just don't know where to look. I am guessing it is just where the wire is hooked up on there that tells the fan what speed to run at.[url=http://climatedoctors.zoovy.com/product/ICM24/ICM280_Goodman_Furnace_Control_Circuit_Board.htmlLinky[/url]

I think I also might have found some type of manual or something, but I don't see the specs for LP listed there.

[Brian Hampton]

Hey,

Maybe not useful but thought I should mention.... Maybe something about the heating system is loose and therefore vibrating more then it should and making it louder.

I became a home owner a few years back and our heating system (oil boiler) would wake me up in the night even though it was in the basement and I was in the second floor. There's lots of panels and covers and stuff on the system and I noticed by putting pressure on some of these by hand when it was ruinning the system got much quieter. I then re-seated or tightened down a few things and it was much quieter.

-Brian

EDIT- Now that I think about the "blower" part a bit... That blower motor may have bushings to mount which need to be replaced or serviced or maybe it could be time for a new one.

[paw]

I'd just turn off the furnace. There's no room to modify the return. Though if you wake up cold, don't blame us.

If you want to be more sophistcated, use Mark's (mhalsan) relay idea.

[ronronzz]

[loribates]

Wow.... I love my boiler.
Aside from the fact I still get heat gain of about 5 degrees even after the boiler shuts off (BONUS!!). Nothing but a whoosh when it lights and a little whirring of the water through the radiators. I only hear it late at night when I'm falling asleep. I have the same trouble as you though because I do have a central AC in the basement so during the summer when that's running it can really peeve you off during a movie. I just shut it off. If and when you find a solution I'm looking forward to seeing what you come up with.

[AnalogRocks]

Neat! This thread was resurected 365 days later.

[AnalogRocks]

Neat! This thread was resurected 365 days later.

[jkruger]